Conventionally, in a plant and a factory, a distributed control system (DCS) is established in order to implement advanced automatic operations. Field devices (a measurement device and an operation device) and controller controlling them are connected to each other in the distributed control system. The field device included in the distributed control system performs wire communications. However, in recent years, a wireless field device which performs wireless communications in conformity with industrial wireless communication standards, such as ISA100.11a and WirelessHART (registered trademark), is realized.
An input/output part, a wireless communicator, and a controller are disposed in a case of the above-described wireless field device. The input/output part generally performs measurement or operation of state quantity (for example, pressure, temperature, and flow quantity) in an industrial process. The wireless communicator performs wireless communications in conformity with the above-described industrial wireless communication standards. The controller totally controls operation of the wireless field device, are disposed in a case of the above-described wireless field device. Moreover, the each part of the wireless field device is operated by electric power supplied from a single power source. Here, it is not necessary to connect the wireless field device to a communication line or a communication bus, like a conventional field device, and the wireless field device is basically installed in a plant independently. For the reason, the wireless field device is equipped with a battery as the single power source.
The following patent document 1 discloses that a wireless device is attached to the conventional field device which does not have a wireless communicator, and the wireless device is capable of operating the conventional field device as a wireless field device. Specifically, the wireless device disclosed in the following patent document 1 includes an interface, a wireless communicator, and a power source. The interface is connected to the conventional field device. The wireless communicator performs wireless communications. The power source supplies electric power to the conventional field device through the interface. In a case that a signal from the field device is input to the wireless device through the interface, the wireless device transmits the signal from the wireless communicator to a transmission destination (for example, a host controller). In a case that the wireless communicator receives a signal of which destination is the field device, the wireless device outputs the received signal to the field device through the interface.